Exhaust gas muffler

ABSTRACT

An exhaust gas muffler for an engine, the exhaust gas muffler having a body, at least one inlet for the exhaust gas from the engine on the body, a baffled chamber in the body to receive exhaust gas from the at least one exhaust gas inlet, at least one exhaust gas outlet from the baffled chamber to vent the exhaust gas from the baffled chamber, at least one fresh-air inlet on the body, a heat exchange conduit extending into the baffled chamber between the fresh air inlet and the at least one exhaust gas outlet, the heat exchange conduit being sized and shaped to permit heat exchange between the fresh air and the exhaust gas in the baffled chamber, and a fresh air outlet on the heat exchange conduit, the fresh air outlet being sized, shaped and located relative to the exhaust gas outlet to permit the fresh air to mix with exhaust gases being vented from the baffled chamber to lower an exit temperature of the exhaust gases.

FIELD OF THE INVENTION

This invention relates to the general field of exhaust systems, and moreparticularly to mufflers used with internal combustion engines.

BACKGROUND OF THE INVENTION

Internal combustion engines generate by products of combustion oftenreferred to as exhaust gases. Typically, for noise control the exhaustgases pass through a muffler and tailpipe before being released. Suchengines and their associated exhaust systems are ubiquitous, being usedto power all types of motor vehicles as well as smaller, morespecialized vehicles and devices such as, for example, golf carts,ATV's, lawn tractors, power generators, and other turf and industrialequipment.

The exhaust gases from an internal combustion engine can be very hot,for example, over 1000° F. Such high temperatures can affect mufflercomponents, in particular causing mufflers to wear out and requirereplacement faster than otherwise. Another problem is that the highexhaust temperature may cause“after bang” or “back firing” when unburntor semi-burnt hydrocarbons, which may be contained in the flow areignited upon contact with hot muffler components. High exhausttemperatures therefore are a potential safety hazard.

In conventional passenger and truck motor vehicles the exhaust gasesgenerally cool to some extent through a long exhaust pipe between theengine and muffler. In smaller vehicles the exhaust pipe is likely to beshort, with correspondingly hotter exhaust gases received by themuffler. Also, since the motor compartment in smaller vehicles is morecrowded, the heat emanating from a very hot muffler is more likely tohave an adverse affect on the performance or durability of neighbouringcomponents. Thus, problems of high temperature exhaust gases can be moreacute in smaller vehicles and motors. In many smaller motorized deviceapplications the muffler may be somewhat exposed. As such, the muffler,if it gets very hot, becomes a safety hazard to users of the motorizeddevice. One solution is for such mufflers to be built with an insulateddouble layer outer wall. This type of muffler lowers the surfacetemperature of the muffler, which usefully helps prevent burns to userswho may have incidental contact with the muffler and also reduces heatdamage to neighbouring components. However, the outer insulation in thistype of muffler also magnifies the problem of high internal and tailpipeexit temperature for the exhaust gases.

Such problems have led to a different approach, which is disclosed inU.S. Pat. No. 4,265,332 to Presnall. This patent shows a mufflersurrounded by a heat shield that defines an annular air passage 68around the outer surface of the muffler. At the tailpipe output of themuffler the heat shield narrows. When in use, the exhaust gases exitingthe tailpipe pass out the muffler and through the narrow part. Thisdraws ambient air through the air passage 68. The ambient air flow coolsthe body of the muffler as it contacts the muffler's hot outer surface.The ambient air continues to flow around the muffler until it mixes-withthe exhaust gases to cool the exhaust gas output. Similar devices thatalso use an external heat shield, and that draw air through an air gapconcentric to the muffler by means of a narrow venturi at the exhaustgas exit are shown in U.S. Pat. No. 4,741,411 to Stricker and U.S. Pat.No. 4,487,289 to Kicinski.

While these devices produce some cooling, the effect is limited sincethe cool air only passes past the outer skin of the muffler. The hotexhaust gas inside the muffler is relatively unaffected. Further, theexternal heat shield adds bulk to the muffler, which can be a problemparticularly in smaller vehicles where the space is not available. Thismay force a costly redesign of the motor compartment and lead to alarger overall device. Also the external heat shield adds weight andexpense to the muffler, and is not that easy to fabricate. Accordingly,in the absence of a more effective solution the durability and safetyproblems inherent to mufflers operating with high temperature exhaustare likely to continue.

SUMMARY OF THE INVENTION

What is desired is an exhaust muffler which overcomes one or more of theproblems associated with the current devices and methods used forcooling exhaust mufflers.

Preferably, the operating temperature inside the muffler will bereduced, so that the muffler components are subjected to less heatstress and thereby achieve enhanced durability. The temperature of theexhaust gas output from the muffler will preferably also be reduced,producing a corresponding reduction in the risk of ignition of foreignmaterials and of back firing. It would be preferable as well if a heatshield or other bulky external device is not required, so that themuffler may be made as small as possible and thus more easily integratedinto the existing motor compartments of the various internal combustionengine vehicles and devices.

Therefore, there is provided, according to a first aspect of the presentinvention, an exhaust gas muffler for an engine, said exhaust gasmuffler having:

-   -   a) a body;    -   b) at least one inlet for said exhaust gas from said engine on        said body;    -   c) a baffled chamber in said body to receive exhaust gas from        said at least one exhaust gas inlet;    -   d) at least one exhaust gas outlet from the baffled chamber to        vent said exhaust gas from said baffled chamber;    -   e) at least one fresh-air inlet on said body;    -   f) a heat exchange conduit extending into said baffled chamber        between said fresh air inlet and said at least one exhaust gas        outlet, said heat exchange conduit being sized and shaped to        permit heat exchange between said fresh air and said exhaust gas        in said baffled chamber; and    -   g) a fresh air outlet on said heat exchange conduit, said fresh        air outlet being sized, shaped and located relative to said        exhaust gas outlet to permit said fresh air to mix with exhaust        gases being vented from said baffled chamber to lower an exit        temperature of said exhaust gases.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made, by way of example only, to drawingsillustrating the preferred embodiments of the invention, in which:

FIG. 1 is a side cross-sectional view of the exhaust muffler of thepresent invention;

FIG. 2 is a side cross-sectional view of another embodiment of theexhaust muffler of the present invention;

FIG. 3 is a side cross-sectional view of another embodiment of theexhaust muffler of the present invention;

FIG. 4 is a side cross-sectional view of another embodiment of theexhaust muffler of the present invention;

FIG. 5 is a side cross-sectional view of another embodiment of theexhaust muffler of the present invention; and

FIG. 6 is a side cross-sectional view of another embodiment of theexhaust muffler of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The exhaust muffler of the present invention is shown in a sidecross-sectional view in FIG. 1 and generally designated as 10. Theexhaust muffler 10 generally comprises a body 12, at least one inlet 14,a baffled chamber 16, at least one exhaust gas outlet or tailpipe 18, atleast one fresh-air inlet 20 on the body 12, a heat exchange conduit 22,and a fresh-air outlet 24. The baffled chamber 16 includes at least onebaffle 26, and the fresh-air inlet 20 usually includes an air filter 28.The tailpipe 18 has an input end 19 inside the baffled chamber 16 and anoutput end 21 located outside the muffler 10.

The exhaust muffler 10 receives exhaust gas 30 through the inlet 14 andambient air 32 through the fresh-air inlet 20. The exhaust gas 30 andambient air 32 are shown as a series of arrows indicating the generalflow of the gas and air through the device 10. For additional clarityand to distinguish the two gases, the exhaust gas 30 is represented byan open arrowhead and the ambient air 32 is represented by a closed,triangular shaped arrowhead. It can be seen from FIG. 1 that the ambientair 32 flows from the fresh-air inlet 20 through the heat exchangeconduit 22 and fresh-air outlet 24 into the exhaust gas outlet ortailpipe 18, and is eventually expelled at the tailpipe output 21.

The exhaust muffler 10 of the present invention receives the exhaust gas30 through attachment of the inlet 14 to an exhaust pipe carrying thegas away from an internal combustion engine (not shown). The exhaust gas30 is the well-known gas produced by the engine upon completion of acycle of combustion. This gas is generally very hot, for example, 1000°F. or more, and contains byproducts of combustion. The exhaust gas 30flows through the baffled chamber 16 into the tailpipe input 19, and outof the muffler 10 at the tailpipe output 21. As is well known, the flowof gas 30 within the muffler 10 acts to reduce the loud sound or noiseof the engine. In addition, the muffler 10 of the present inventionfunctions to reduce the internal temperature of the muffler inside thebaffled chamber 16, and also to reduce the temperature of the exhaustgas 30 at the tailpipe output 21.

The body 12 of the muffler 10 of the present invention may be anyhousing or enclosure adapted to receive hot exhaust gases ejected froman internal combustion engine. In most cases a body constructed from14-22 gauge mild, aluminized or stainless steel has been found to beadequate. The outer walls of the body 12 will commonly be a single layeror double layer with or without separation by insulating material havingthe thickness of the gauge of steel being used.

The body 12 can be rectangular, oval, cylindrical, or any other shape.However, as will be appreciated by those skilled in the art, the body 12will be sized and shaped to handle the exhaust gases being generated bya specific motor, and that can be installed in the motor compartmentspace available. For many small vehicle applications the muffler body 12will be in the range of about 8 to 16 inches.

The present invention comprehends that the inlet 14 may be any form ofconduit, tube, or other device on the body 12 that is adapted to receivethe exhaust gas 30 from the engine. While there will be at least oneinlet 14, it can be appreciated that some embodiments of the muffler 10will have multiple inlets 14. In the preferred embodiment the inlet 14is a tube welded or attached to a hole through a side wall of the body12. Most preferably the tube is sized and shaped to form a secure andairtight fit with an engine exhaust pipe or outlet, and extends bothinwardly and outwardly from the body.

The baffled chamber 16 defines a space in the interior of the body 12that receives the exhaust gas 30 from the exhaust gas inlet 14. Thebaffle 26

is a sheet or plate, generally constructed of the same material steel asthe body 12, that divides the chamber 16 into at least two internalcompartments 34. There is at least one opening or hole 36 in the baffle26 to enable the exhaust gas 30 to pass between the internalcompartments 34. While the baffle 26 will most commonly be a singlelayer, a double or multiple baffle 26 such as that shown in FIG. 4 canalso be used.

In FIG. 1 the single baffle 26 divides the chamber 16 into twocompartments, designated first internal compartment 34 a and secondinternal compartment 34 b. It can be appreciated that adding morebaffles will increase the number of compartments 34 and the level ofsound attenuation performed by the muffler 10. FIG. 2 shows an exampleof a muffler 10 having two baffles 26 and three compartments designatedas first, second, and third internal compartments 34 a, 34 b, and 34 crespectively. Similarly, a muffler having three baffles will be dividedinto four compartments 34. Of course, more chambers may be used ifdesired, and various forms of baffles and other muffling material mayalso be used in the chamber.

The present invention comprehends that the exhaust gas outlet ortailpipe 18 is a conduit, tube, or other device sized and shaped to ventthe exhaust gas 30 from the baffled chamber 16 to the ambient airoutside the muffler 10. In the preferred embodiment the tailpipe 18 is aconduit or tube made of an appropriate material as discussed above, thatextends from the tailpipe input end 19 inside the baffled chamber 16through a wall of the body 12 to tailpipe output end 21 outside themuffler 10. In this way, exhaust gas 30 and ambient air 32 that flowinto the tailpipe 18 inside the baffled chamber 16 are able to flowoutside.

As will be discussed in greater detail below, according to the presentinvention, that portion of the exhaust outlet 18 inside the baffledchamber 16 is sized and shaped to promote heat transfer between theexhaust outlet 18 and the exhaust gas 30 that is in the internal chamber34 to which the exhaust outlet 18 is attached.

The present invention further comprehends that the fresh-air inlet 20may be any passageway, conduit, tube, or other device on the body 12that is adapted to receive the ambient air 28 from the atmosphereoutside the muffler 10 and convey it to the heat exchange conduit 22.The fresh-air inlet 20 may accordingly be a tube welded or attached to ahole in the body 12, with an opening inside the body 12 that is sizedand shaped to receive the heat exchange conduit 22. However, asdiscussed below, the fresh-air inlet 20 is preferably simply an outer orexternal end of the heat exchange conduit 22. This embodiment ispreferred since it is a simpler configuration, requiring only oneelement instead of two, and since there would be no issue of interfacingthe fresh-air inlet 20 with the conduit 22.

As shown in FIG. 1, the fresh-air inlet 20 preferably also includes theair filter 28 to prevent unwanted material such as grass, dirt, stones,and other airborne debris from entering or being drawn into the heatexchange conduit 22. The air filter 28 may be a screen, such as a wiremesh screen, a one-way baffle, or functionally any type of deviceconfigured to pass air but block physical particles larger than apredetermined minimum size. The air filter 28 may be attached to thefresh-air inlet 20 through any one of a number of well-known means suchas a screw, bolt, or welded connection. Preferably the attachment isreleasable so that the air filter 28 can be easily removed and cleaned,or replaced if damaged.

The heat exchange conduit 22 is a passageway, conduit, or tubeconfigured to extend within the baffled chamber 16 between the fresh-airinlet and the exhaust gas outlet 18. The heat exchange conduit 22 can beof any convenient shape or length, as long as it functions to provide aconnecting passage to carry ambient air 32 from the fresh-air inlet 20to the exhaust gas outlet 18. Preferably the conduit 22 will beconstructed from tubular steel, but it can be appreciated that othermaterials that are heat conductive, lightweight, durable, and that canfunction in a high temperature environment are also comprehended.

As noted, the heat exchange conduit 22 carries ambient air 32 inside abaffled chamber 16 filled with exhaust gas 30. Since the exhaust gas isinvariably extremely hot, i.e. on the order of about 1000° F., theambient air 32 will always be much cooler than the temperature insidethe baffled chamber 16. Therefore, a process of heat exchange will occurbetween the hot exhaust gas 30 and the heat exchange conduit 22. In thisprocess, a portion of the extreme heat of the gas 30 will transfer tothe ambient air 32 inside the heat exchange conduit 22 and move out ofthe muffler 10 as the ambient air 32 flows out of the tailpipe output21. This has the desirable effect of lowering the internal temperatureof the muffler 10. Accordingly, the heat exchange conduit 22 will besized and shaped to permit heat exchange between the fresh ambient air32 and the exhaust gas 30 in the baffled chamber 16.

The present invention comprehends various ways to size and shape theheat exchange conduit 22 to promote such heat exchange in the muffler10. One aspect relates to the material used to construct the conduit 22.The material should be heat conductive so that the heat from the exhaustgas 30 can be efficiently transferred through the wall of the heatexchange conduit 22 to the ambient air 32. Another aspect relates toenhancing heat exchange by decreasing wall thickness of the conduit 22.Accordingly, the material should also be sufficiently strong so that thewall of the conduit 22 can be made as thin as possible, In the preferredembodiment, the tubular steel used is both a good conductor of heat andcan be fashioned into a tube having an adequately thin wall, while stillretaining intrinsic strength. It can be appreciated that other metals,and other good heat conductive, thin-walled materials may also beadequate as long as they satisfy the other desirable attributes of beinglightweight, durable, and effective in a high temperature environment.

A further aspect of promoting heat exchange relate to surface featuresof the heat exchange conduit 22. Heat exchange is enhanced when thesurface area between the hot and cold areas across which the exchangetakes place is maximized. Accordingly, adding exterior surface featuressuch as fins to the conduit 22, in order to increase the effectivesurface area of the conduit 22, is generally desirable. It can beappreciated that other types of surface features besides fins might alsobe used with adequate results.

Apart from fins or the like, the present invention also comprehendssizing the conduit and positioning the baffle in the baffled chamber sothat more cool surface area is exposed for heat exchange. For example,FIGS. 5 and 6 show a design using a relatively narrow diameter heatexchange conduit 22, of the type suitable for lower horsepower motorsneeding less air flow. The narrower conduit has a relatively smallersurface area than conduits having a wider diameter, such as those shownin FIGS. 1 and 2. It can be seen that in FIGS. 5 and 6 the internalcompartment 34 a is relatively long, so that the hot exhaust gas 30 cancontact a greater length of heat exchange conduit 22, to offset theeffect on heat transfer rates of a smaller surface area of the conduit.

It has also been found that heat exchange between gases is improved whenone or both of the gases are turbulent. The hot exhaust gas 30 isgenerally turbulent simply by the nature of the process of injectingexhaust gas 30 into the baffled chamber. The ambient air 32 flowinginside the heat exchange conduit generally follows a laminar flow, butcan be encouraged to become turbulent by modifying the surface featuresor textures of the interior of the conduit 22. This may include, forexample, raised bumps or dents along the inner surface. Such featureswill disrupt the smooth flow of ambient air 32 and encourage turbulence,thus improving heat transfer rates.

Yet another aspect is that heat exchange is enhanced as the temperaturedifferential or contrast between the hot and cold surfaces increases.Therefore, a given heat exchange system can operate closer to optimumefficiency if it is designed to maximize the exposure of the hottestfluid with the coldest fluid across a heat exchange surface. In themuffler 10 of the present invention, this is achieved by directing thehot exhaust gas 30 from its point of exit from the exhaust inlet 14,where the gas 30 is hottest, onto the heat exchange conduit 22,particularly in the internal compartment 34 a where the conduit 22 isimmediately attached or adjacent to the fresh-air inlet 20. The conduit22 will be coldest at this point, where it has just received ambient air32. This can be seen in the design of FIG. 3, which shows the exhaustgas inlet 14 directed at the heat exchange conduit 22, and where theconduit 22 has been positioned in the middle of the body 12 so that thetwo elements are positioned adjacent to one another. FIG. 4 shows avariation where the exhaust gas inlet 14 is at the end and the conduitenters from the bottom and curves to meet the exhaust gas outlet 18.Again the inlet 14 is directed at the heat exchange conduit 22 a shortdistance away to promote heat exchange between the exhaust gases 30 andthe fresh air 32 in the heat exchange conduit when the muffler is inuse. The exhaust gas inlet 14 can also be directed at the tailpipe 18 topromote heat exchange, since there will be a temperature differentialbetween the hot exhaust gas 30 entering the baffled chamber 16 and theexhaust gas 30 inside the tailpipe 18 which has been cooled by mixturewith the ambient air 32. This may be seen in FIG. 2, which shows exhaustgas inlet 14 b directed at tailpipe 18.

It can be appreciated that the exterior and interior surface featuressuch as fins, bumps, or dents described above add to the cost of theheat exchange conduit 22. As well, the choice of material will likelyinvolve cost considerations, and the layout of the conduit 22 relativeto the inlet 14 may be governed in part by the overall vehicleapplication and motor compartment space available. Accordingly, it canbe appreciated that the design of the muffler 10 of the presentinvention will involve careful consideration of the various factors inorder to maximize heat exchange within the constraints that may beimposed by cost and the parameters of the particular design.

The fresh-air outlet 24 is a passageway, conduit or tube attached to,on, or part of the heat exchange conduit 22, that receives the ambientair 32 from the conduit 22 and transmits it to the tailpipe 18 at thetailpipe input 19. In particular, the fresh-air outlet 24 is sized,shaped, and located relative to the exhaust gas outlet 18 to permit thefresh ambient air 32 to mix with the exhaust gases 30 being vented fromthe baffled chamber 16, to lower an exit temperature of the exhaustgases 30. Preferably, the fresh-air outlet 24 is sized and shaped to fitwithin at least a portion of the tailpipe 18, in particular at thetailpipe input end 19.

Preferably, as shown in all of the FIGS. 1-6, the fresh-air outlet issimply a terminal end of the heat exchange conduit 22. In that case, thefresh-air outlet 24 is that portion of the conduit 22 that interfaces oroverlaps with the tailpipe 18. In FIGS. 1-4 it can be seen that the heatexchange conduit 22 and tailpipe 18 are of approximately the samediameter. Accordingly, in these embodiments the conduit 22 tapers toform the fresh-air outlet 24, which is a narrower portion that fitswithin the tailpipe 18 at the tailpipe input end 19. In anotherembodiment shown in FIGS. 5 and 6, the heat exchange conduit 22 has adiameter uniformly narrower than the diameter of the tailpipe 18. Inthat case the fresh-air outlet 24 comprises an end portion of theconduit 22 which again fits inside the tailpipe 18 at the tailpipe inputend 19. In both cases the exhaust gas 30 enters the tailpipe 18 throughan annulus 38, which is the concentric space between the outer diameterof the fresh-air outlet 24 or terminal end of the conduit 22 and theinner diameter of the tailpipe input end 19.

The muffler 10 of the present invention also includes a means to pull ordraw the fresh or ambient air 32 into the fresh-air inlet 20 on the heatexchange conduit 22. The means moves the ambient air 32 through theconduit 22 and fresh-air outlet 24, and into the tailpipe 18. This airpulling or air drawing means can be anything that draws in air,including, for example, forced air systems such as fans, blowers, orsuction lines.

Preferably however the means is a low pressure area created by a simpleventuri. A venturi is preferred over forced air systems because it is apassive system that has no moving parts.

A venturi is a tube with a constriction or a small diameter flow area.When a gas or other fluid flows through a venturi it will tend to speedup, to maintain an even flow through the tube. According to theBernoulli principle, when a gas or fluid speeds up a low pressure areaor region is created.

Turning to FIG. 1, it can be seen that a venturi is created at thetailpipe input end 19 due to the orientation of the fresh-air outlet 24of the heat exchange conduit 22 with the tailpipe 18. In particular, asdescribed above an annulus or venturi 38 is created between the narrowerfresh-air outlet 24 and tailpipe 18. The venturi 38 is a constriction inthe flow of exhaust gas 30, which otherwise, in a conventional muffler,would be able to flow through the full diameter of the tailpipe 18. Asthe exhaust gas 30 passes through the venturi 38, it speeds up andcreates a low pressure region 40 in front of the fresh-air outlet 24.This region 40 is broadly in the shape of a cone or 20 triangle. Theexhaust gas 30 that flows into the tailpipe 18 will tend to bend aroundthe low pressure region 40 as it flows towards the tailpipe output end21. At the same time, the low pressure region 40 acts to pull or draw inambient air 32 through the fresh-air inlet 20 and heat exchange conduit22.

The venturi 38 can also have any shape that is convenient to fit theparticular tailpipe and muffler configuration, provided a sufficientlyreduced area flow cross-section is presented to create the preferred lowpressure region 40. Therefore, as shown in FIGS. 1-4, the venturi 38 maybe formed between a narrow tapered fresh-air outlet 24 on the heatexchange conduit 22 and the exhaust gas outlet 18. In anotherembodiment, as shown in FIGS. 5-6, the heat exchange conduit 22 has auniform diameter adjacent to the fresh-air outlet 24, and the exhaustgas outlet 18 is sized and shaped to fit around the fresh-air outlet 24to form the venturi 38. In the embodiment of FIG. 6, the tailpipe inputend 19 is perforated adjacent to the venturi 38, to allow for the entryof exhaust gas 30 into the tailpipe 18.

It can be appreciated that the degree of low pressure created by the lowpressure region 40 is inversely related to the size of the annulus orventuri 38. As the size of the venturi 38 is reduced, as for example bysubstituting a larger fresh-air outlet 24, a lower pressure low pressureregion 40 is created which draws in a larger volume of ambient air 32.While a larger air flow is generally desirable, if the size of theannulus 38 is reduced too much an undesirable back pressure arises whichcan block or hinder the flow of exhaust gas 30 from the engine. This canhurt engine performance. Therefore the annulus 38 should not be so smallas to create too high a back pressure. By contrast, if the annulus orventuri 38 is too large, which may occur when, for example, thefresh-air outlet 24 is relatively small, the speed of ambient air 32into the heat exchange conduit 22 may be substantially reduced and themuffler 10 won't cool as efficiently. Therefore, the venturi 38 shouldbe designed so that the cooling function is optimized without creatingunacceptable back pressure.

It can be appreciated that when the muffler 10 is in use, the venturi 38of the present invention is adapted to continuously draw in more ambientair 32 as more exhaust gas 30 is vented. Further, the venturi 38 willdraw in the ambient air 32 at a greater rate when the exhaust gas 30 isvented at a greater rate. Accordingly, the venturi 38 may be viewed ashaving an inherent self regulating capability in that it will generallydraw in an appropriate amount of fresh air, proportionate to the demandsof the engine.

In the preferred embodiment of the invention, it was found that avariety of tube sizes provided adequate results. These include, forexample, a muffler having a tailpipe 18 with an inner diameter of 1.125inches and a heat exchange tube with a reduced fresh-air outlet sectionof 0.875 inches (plus wall thickness 0.048″), and another similarmuffler with corresponding measurements of 1.13 inches for the tailpipeand 0.8 inch (plus wall thickness 0.048″). The uniform narrow diameterembodiment of FIGS. 5 and 6 produced adequate results with a tailpipe of1.255 inches inner diameter and a heat exchange tube of 0.625 inches(plus wall thickness 0.048). Using a 16 HP engine running at an enginespeed of 3600 rpm, an air velocity of 1500 feet/minute was reached inthe heat exchange tube 22. It can be appreciated that other tube sizesand engine speeds may also be used that would produce adequate results.

It can be appreciated that the muffler 10 of the present invention canbe simply and easily manufactured using known methods and techniques. Inparticular, the elements of the body 12, exhaust gas inlet 14, baffledchamber 16, and tailpipe 18 may be readily constructed. As noted above,the elements of the fresh-air inlet 20, heat exchange tube 22, andfresh-air outlet 24 are preferably in the form of a single conduit ortube, where the fresh-air outlet 24 may be a reduced or narrowedsection. Accordingly, the combined unit, designated as conduit 22, maybe installed in the muffler 10 in a manner similar to that used toinstall the tailpipe 18. The additional holes to be made in the body 12and baffle 26 to accommodate the conduit 22 are also similar to theholes made for the tailpipe 18.

It is preferable that the conduit 22 be installed so that the fresh-airoutlet 24 is well centered and concentric with the tailpipe input end19. If the tubes are off-center the low pressure region 40 will be lesseffectively formed. This will cause less ambient air 32 to be drawn in,and the overall cooling efficiency of the muffler 10 will be reduced.

The operation of the present invention can now be described. When theinternal combustion engine is operating, hot exhaust gases 30 will flowinto the exhaust gas inlet 14 and the baffled chamber 16, raising theinternal temperature of the muffler 10. The gases will-circulate betweenthe internal compartments 34, passing through the openings 36 in thebaffles 26. The exhaust gases 30 will enter the venturi 38 createdbetween the fresh-air outlet 24 and the tailpipe input end 19 and speedup as they pass through the venturi. This will create a low pressureregion 40 inside the tailpipe 18 at the front of the fresh-air outlet24. The low pressure region 40 will draw or pull in ambient air 32through the air filter 28, fresh-air inlet 20, heat exchange conduit 22,and fresh-air outlet 24. The ambient air 32 will continue into thetailpipe 18, where it will mix with the exhaust gas 30 until the gas 30and air 32 are vented into the atmosphere at tailpipe output end 21. Asmore exhaust gas is vented more fresh air is pulled in. Further, as thepower of the engine varies changing the rate at which the exhaust gasvents, the rate at which fresh air is pulled in will also vary inproportion. In this way the cooling effect will be maintained.

The ambient air 32 drawn into the heat exchange conduit 22 will besubstantially cooler than the exhaust gas 30. A process of heat exchangeor conduction will take place between the hot exhaust gas 30 and therelatively cool heat exchange conduit 22. This process may befacilitated or promoted by design of various features of the heatexchange conduit 22 as discussed above. In the heat exchange, the coolerambient air 32 will draw heat from inside the muffler 10 and dischargeit through the tailpipe 18. Since the ambient air 32 enters the tailpipe18 where it mixes with exhaust gas 30, the tailpipe 18 will also becooled relative to the muffler internal temperature, though not to thesame extent as the heat exchange conduit 22. Therefore, heat exchange orconduction will also take place between the tailpipe 18 and the exhaustgas 30.

Turning to FIG. 1, it can be seen that internal compartment 34 a will becooled by conduction from the heat exchange conduit 22, and thatinternal compartment 34 b will be largely cooled by conduction fromtailpipe 18. Similarly, in the two baffle embodiment of FIG. 2, it canbe seen that internal compartment 34 a will be cooled by conduit 22,compartment 34 b will be cooled by both conduit 22 and tailpipe 18, andcompartment 34 c will be cooled by conduction with tailpipe 18.

It can therefore now be appreciated how the the operating temperatureinside the muffler will be reduced. The lower internal temperaturegenerally has the effect of subjecting the muffler components to lessheat stress, so that they achieve enhanced durability. It can also beappreciated that the temperature of the gas vented at the tailpipeoutput end 21 will be reduced because of the presence of the mixed-inambient air 32. The lower temperature at the tailpipe output reduces therisk of ignition of foreign materials and of back firing.

Testing of the present invention was carried out on a muffler having atwo-baffle embodiment similar to that shown in FIG. 2. The engine usedwas a 23 HP engine running at a power of 60% and 70% of capacity. Theobserved temperatures at each power output level were recorded usingfirst a reference muffler not having the heat exchange conduit 22 of thepresent invention, and then again using the muffler 10 of the presentinvention.

Upon review, it was found that in the internal compartment 34 a thetemperature was reduced on average by about 234° F., in the middleinternal compartment 34 b temperature was reduced by about 17° F., andin internal compartment 34 c temperature dropped by about 37° F. At thetailpipe output end 21 the exhaust gas temperature was reduced by about225° F.

It can now be appreciated that the present invention is suitable for usewith internal combustion engine driven vehicles and devices that use amuffler, and that it is particularly suitable for those that are fairlycompact, so that the muffler is close to the engine and the exhaustgases remain quite hot at the entry to the muffler. It can also now bereadily appreciated that the muffler 10 of the present invention may beeasily integrated into the existing motor compartments of the variousvehicles and devices, as it has the same basic form factor or shape asconventional mufflers and does not require a heat shield or other bulkyexternal device.

It will be appreciated by those skilled in the art that the foregoingdescription was in respect of preferred embodiments and that variousalterations and modifications are possible within the broad scope of theappended claims without departing from the spirit of the invention. Forexample, while reference is made to tubular conduits, other shapes andsizes of conduits might also provide reasonable results. Further,different means may be used to improve heat exchange, as taught herein,without departing from the scope of the present invention. Various othermodifications will be apparent to those skilled in the art but are notdescribed in any further detail herein.

1. An exhaust gas muffler for an engine, said exhaust gas mufflerhaving: (a) a body; (b) at least one inlet for said exhaust gas fromsaid engine on said body; (c) a baffled chamber in said body to receiveexhaust gas from said at least one exhaust gas inlet; (d) at least oneexhaust gas outlet from the baffled chamber to vent said exhaust gasfrom said baffled chamber; (e) at least one fresh-air inlet on saidbody; (f) a heat exchange conduit extending into said baffled chamberbetween said fresh-air inlet and said at least one exhaust gas outlet,said heat exchange conduit being sized and shaped to permit heatexchange between said fresh air and said exhaust gas in said baffledchamber; and (g) a fresh air outlet on said heat exchange conduit, saidfresh air outlet being sized, shaped and located relative to saidexhaust gas outlet to permit said fresh air to mix with exhaust gasesbeing vented from said baffled chamber to lower an exit temperature ofsaid exhaust gases. 2-19. (canceled)
 20. A method of cooling an exhaustgas inside of a muffler body, said method comprising the steps of: (a)cooling said exhaust gases by conduction in at least a first internalmuffler chamber by exposing said exhaust gases in said first mufflerchamber to a heat exchange surface cooled by cooling air; and (b)further cooling said exhaust gases by mixing said exhaust gases withsaid cooling air inside said muffler, before said exhaust gases arereleased from said muffler.
 21. A method as claimed in claim 20 furtherincluding the step of drawing said cooling air into said muffler pastsaid heat exchange surface.
 22. A method as claimed in claim 21 whereinsaid step of drawing cooling air into said muffler further comprisesforming a venturi adjacent to a cooling air conduit to create a lowpressure region for drawing in said cooling air.
 23. A method as claimedin claim 22 wherein said step of mixing said exhaust gases with saidcooling air occurs adjacent to said venturi.